We do not claim that databases encountered in practical applications
typically have small cliquewidth. In fact, an empirical study of
real-world databases has found that their treewidth tends to be high
[1]}, and one may expect similar results
for cliquewidth. The same study, however, also points out the
opportunities that lie in the decomposition of a database into a part
of high treewidth and parts of low treewidth, and this has in fact
been used successfully to implement efficient querying
[2]}, [3]}, [4]}. While
we are not aware that similar approaches based on cliquewidth have yet
been studied, it seems entirely reasonable to pursue them. The work
presented here may provide a foundation for such an
endeavour.
